Flash memory card

ABSTRACT

A Flash memory card is disclosed comprising a substrate, a Flash memory die on top of the substrate, a controller die on top of the Flash memory die, and an interposer coupled to with the controller die and on top of the Flash memory die wherein the interposer results in substantial reduced wire bonding to the substrate. The interposer can surround or be placed side by side with the controller die. A system and method in accordance with the present invention achieves the following objectives: (1) takes advantage of as large of a Flash memory die as possible, to increase the density of the Flash card by reducing the number of wire bond pads on the substrate and enabling insertion of the largest die possible that can fit inside a given card interior boundary; (2) more efficiently stacks Flash memory dies to increase density of the Flash card; and (3) has a substantially less number of bonding wires to the substrate as possible, to improve production yield.

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. §120 the present application is a continuation of U.S.patent application Ser. No. 12/181,721, filed Jul. 29, 2008, entitled“FLASH MEMORY CARD,” which is a continuation of U.S. Pat. No. 7,411,293,issued on Aug. 12, 2008, entitled “FLASH MEMORY CARD,” which is acontinuation-in-part of and claims the benefit of priority to U.S. Pat.No. 7,411,292, issued on Aug. 12, 2008, entitled “FLASH MEMORY CARD,”all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to Flash memory and morespecifically to a high density Flash memory card.

BACKGROUND OF THE INVENTION

A Flash memory card application is driven mainly by consumer electronicsproducts, such as a digital still camera (DSC), cell phone, PDA or MP3player, toward a smaller form factor and high density. As the formfactor becomes smaller while the density requirement grows higher, aneed is created for innovative approaches to include as many Flashcomponents into a limited space within the boundary of a particularFlash memory card.

Conventional approaches to pack more density into a Flash memory cardare accomplished through wire bonding of one or more Flash memory diesand a Flash controller. A Flash memory die is usually much larger than aFlash controller die in physical size. The Flash memory dies and Flashcontroller are individually wire-bonded onto a substrate of the Flashmemory card.

The substrate usually has interconnecting traces that serve to connectsignals among the Flash controller, Flash memory dies and Flash cardinterface. The substrate is then molded with resin or covered withexternal casing and made into a finished Flash memory card.

For example, if there are approximately 40 signals and pads on thecontroller and approximately 20 signals and pads on each Flash memorydie, placement constraints are created if both the Flash controller dieand Flash memory dies are to be interconnected through wire bonding tothe base substrate. Typically 60 pads on the substrate are required forone Flash memory die design and 20 more pads for each additional Flashmemory die that is stacked. Therefore, the Flash memory die sizes haveto be smaller to leave spaces for the wire bond pads. Furthermore,production yield problems are created due to the necessity of staggeringbonding wires from multiple layers of dies.

Accordingly, what is needed is a system and method for providing a highdensity, small form factor Flash memory card which addresses theabove-identified issues. The system should be easy to implement, costeffective and adaptable to existing systems. The present inventionaddresses such a need.

SUMMARY OF THE INVENTION

A Flash memory card is disclosed comprising a substrate, a Flash memorydie on top of the substrate, a controller die on top of the Flash memorydie, and an interposer coupled to with the controller die and on top ofthe Flash memory die wherein the interposer results in substantialreduced wire bonding to the substrate. The interposer can surround or beplaced side by side with the controller die. A system and method inaccordance with the present invention achieves the following objectives:(1) takes advantage of as large of a Flash memory die as possible, toincrease the density of the Flash card by reducing the number of wirebond pads on the substrate and enabling insertion of the largest diepossible that can fit inside a given card interior boundary; (2) moreefficiently stacks Flash memory dies to increase density of the Flashcard; and (3) has a substantially less number of bonding wires to thesubstrate as possible, to improve production yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows Flash memory card architecture.

FIG. 2 shows a top view of wire-bonded substrate of a Flash memory card(prior art).

FIG. 3 shows a cross section view of wire-bonded substrate of a Flashmemory card (prior art).

FIG. 4 shows a top view of staggered bonding wires from multiple layersof dies (prior art).

FIG. 5 is a cross section view of staggered bonding wires from multiplelayers of dies (prior art).

FIG. 6 is a top view of an on-die-interposer having a center cut out toaccommodate Flash controller die.

FIG. 7 is a cross-section view of an on-die interposer having a centercut out to accommodate Flash controller die.

FIG. 8 is a cross-section view of stacking two Flash memory dies design.

FIG. 9 is a side view of stacking two Flash memory dies design where theserpentine interposer is used.

FIG. 10 is a cross section view of stacking three Flash memory diesdesign.

FIG. 11 is a side view of stacking three Flash memory dies design wherethe serpentine interposer is used.

FIG. 12 is a relation curve between pad distance and loop height.

FIG. 13 is a side view of stacking two Flash memory dies design wherethe extended tab interposer is used.

FIG. 14 is a side view of stacking three Flash memory dies design wherethe extended tab interposer is used.

DETAILED DESCRIPTION

The present invention relates generally to Flash memory and morespecifically to a high density Flash memory card. The followingdescription is presented to enable one of ordinary skill in the art tomake and use the invention and is provided in the context of a patentapplication and its requirements. Various modifications to the preferredembodiments and the generic principles and features described hereinwill be readily apparent to those skilled in the art. Thus, the presentinvention is not intended to be limited to the embodiments shown, but isto be accorded the widest scope consistent with the principles andfeatures described herein.

FIG. 1 shows a conventional Flash memory card 10. The Flash memory card10 comprises a Flash card interface 11, a Flash memory controller 12 andone or more Flash memory dies 13. The Flash card interface 11, usuallyin the form of connector or gold finger contacts, serves as acommunication channel to the host devices such as a digital still camera(DSC), cell phone, PDA, MP3 player or PC. The Flash controller 12controls the on-card Flash memory 13 and responds to requests from thehost devices through Flash card interface 11.

In the manufacturing process, the Flash controller 12 and Flash memory13 are mounted on a piece of substrate that has a Flash card interface11 built-in and interconnecting traces in-between the controller 12 andthe Flash memory 13. The Flash controller 12 and Flash memory 13 can bein either bare die form or in a packaged form. The inventionparticularly focuses on the application where at least two bare diesemiconductor components are used and the two components have differentdie sizes.

The conventional Flash memory card that utilizes die form componentstends to adopt one of two approaches in the manufacturing process,called the side-by-side approach and the stacking approach. Bothapproaches will be described herein below.

FIG. 2 shows the top view of a conventional layout of a larger Flashmemory die 23, and a smaller controller die 24 on one side of thesubstrate 22 in a side-by-side approach. FIG. 3 shows a cross-sectionalview of the same arrangement shown in FIG. 2.

In the side-by-side approach shown in FIG. 2, a Flash controller 24 anda Flash memory die 23 are placed side-by-side on a substrate 22. Wires18, 20 and 38 are bonded from both dies on pads 19,27 and 40 to the pads25,26 and 35 on the substrate 22 below, respectively. The substrate 22needs to have about 30 pads to accommodate Flash controller 24connection. An additional twenty 20 pads are required to accommodateFlash memory die 23 connection. As seen in FIG. 3, the substrate 22 islaminated with internal traces 34, 36 and 37 to connect among the Flashcontroller 24, the Flash memory die 23 and the Flash card interface 33.It is a relatively simple process in manufacturing with a side-by-sideapproach. However, this severely limits the die size of Flash memory andFlash controller usable for a given Flash memory card 21, because atotal of 50 bonding wires and pads are required on the substrate 22.

FIG. 4 shows the top view of a conventional layout of a larger Flashmemory die 123, and a smaller Flash controller die 124 on one side ofthe substrate 122 in a stacking approach. FIG. 5 shows a cross-sectionalview of a conventional layout shown in FIG. 4.

In the stacking approach of FIG. 4, a Flash controller die 124 is placedon top of the Flash memory die 123 on a substrate 122. Wires 118, 120and 138 are bonded from both dies on pads 119, 127 and 140 to the pads125, 126 and 135 on the substrate below respectively. Due to multi-layerstacking, staggered wire bonding is necessary. The substrate 122 needsto have about 30 pads to accommodate Flash controller 124 connection. Anadditional 20 pads are required to accommodate Flash memory die 123connection. As seen in FIG. 5, the substrate 122 is laminated withtraces 134 to connect among the Flash controller 124, the Flash memorydie 123 and the Flash card interface 133. This creates a limitation inFlash memory die size, as staggered wire bonding needs more space on thesubstrate 122 to distribute pads and wires. Space to accommodate a totalof 50 additional bonding wires and pads is required on the substrate.Because the Flash controller is placed on top of the Flash memory die,there is less restriction in Flash controller die size compared to thatof the side-by-side approach, where a larger controller die would reducethe size of the Flash as both of them compete for the same, common spaceavailable on the substrate.

The present invention addresses the restrictions of Flash memory diesize in both conventional side-by-side and stacking approaches. Thepresent invention further saves perimeter wire-bond space and simplifieswire-bonding complexity on the substrate. Consequently, larger die sizescontaining more memory capacity can be used in either the side-by-sideor stacking assembly.

A system and method in accordance with the present invention addressesthe above-mentioned problems to achieve the following objectives: (1)Enable placement of the largest Flash memory die possible inside a givengeometry to maximize the density of the Flash card by reducing thenumber of wire bond pads on the substrate. (2) Being able to efficientlystack Flash memory dies if necessary, to increase density of the Flashcard. (3) Having as little bonding wires to the substrate as possible,to improve production yield.

To describe the features of the present invention in more detail, refernow to the following description in conjunction with the accompanyingFigures.

FIG. 6 shows the top view of the Flash memory card in accordance withthe present invention. The layout comprises a larger Flash memory die223, a center cutout interposer 242 and a Flash controller die 224 ontop of the substrate 222. FIG. 7 shows a cross-sectional view of thelayout of FIG. 6.

In this embodiment an interposer 242 is on top of a Flash memory die 223on a substrate 222, as shown in FIG. 6. The interposer 242 is a type ofmaterial similar to the substrate 222 that has bonding pads and ispre-fabricated with connecting traces 243 and 244. It can also be athin, I-metal layer flex circuit made with copper/polyimide. Theinterposer 242 size is just large enough to allow its bonding pads 227to be located next to the exposed Flash die pads 226. The interposer 242has bonding pads 227, 225 conveniently fabricated to be close to thecorresponding pads 226, 219 of the Flash memory die 223 below, and theFlash controller die 224 in the center, respectively, as shown in FIG. 6and FIG. 7. It also has corresponding pads 240 that are convenientlyfabricated to be able to connect the pads 235 on the main substrate 222below the Flash memory die. These wires 238 from the interposer 242 arethe only ones required to connect to the substrate 222 and are in turnconnected to Flash card interface 233 through traces 234 on thesubstrate 222, as shown in FIG. 7.

Unlike the conventional approaches, the present invention shifts almostall wire bonding connection from die to substrate 222 below tointerposer 242 in the middle of Flash card 221. This substantiallyreduces the pad space required on the substrate 222 by changing thenumber of pads on the substrate from in the order of 50 to less than 10,a saving of 80%. This saving in real estate on substrate 222 enablesplacement of a substantially larger Flash memory die previously notpossible due to the space reserved for the bonding pads. Further, withthe usage of interposer 242, the Flash controller die 224 does not needto be placed directly on top of substrate 222. There is, therefore, lessrestriction on the Flash controller die size, which has the same benefitas that of the conventional stacking approach. Typically, this inventionimproves the ratio of Flash memory die size to actual Flash memory cardsize from about 62% to 90% or higher. It allows for a larger Flashmemory die, and therefore a higher density die to be used on the sameFlash memory card 221 design.

In order not to introduce extra height while stacking Flash controllerdie 224 on the interposer 242, that is, sitting on top of Flash memorydie 223, the interposer 242 has a cut-out 228 in the middle area largeenough to accommodate the Flash controller die 224, as shown in FIG. 6and FIG. 7. The Flash controller die 224 sits like an island directly ontop of the Flash memory die 223 instead of on the interposer 242.

If stacking of more Flash memory dies is necessary, then a flexiblecircuit on-die interposer 342 can be used, as shown in FIG. 8 and FIG.9. Note that the flexible interposer 342 can be folded in a serpentinefashion to expand more stacking of Flash memory dies 323, 423 and 523,if necessary, as in FIG. 10 and FIG. 11.

If stacking of more Flash memory dies is necessary, then an extended tabinterposer 344 can be used, as shown in FIG. 13. Additional wire bonding346 is used to connect interposer 344 and 343. If the extended tabinterposer 344 is not stiff enough to perform wire bonding process, astand-off 347 can be added for additional support. Note that theextended tab interposers 348, 349 and wire bonding 351, 352 can be usedto expend more stacking of Flash memory dies 323,423 and 523, ifnecessary, as in FIG. 14. It is optional to use stand-off 353 and 354for additional support for wire bonding process.

FIG. 8 shows the cross sectional view of the layout in accordance withthe present invention with two Flash memory dies 323 and 423, a flexiblecircuit on-die interposer 342 and a Flash controller die 324 on top ofthe substrate 322. FIG. 9 shows a side view of the layout of FIG. 8.

A spacer 345 is necessary between the Flash controller die 324 and theFlash memory die 423 stacking above, as in FIG. 8 and FIG. 9. Anadditional spacer 445 is required if more stacking of Flash memory die523 is needed, as shown in FIG. 10 and FIG. 11.

FIG. 10 shows a cross sectional view of the layout in accordance withthe present invention with three Flash memory dies 323, 423 and 523, aflexible circuit on-die interposer 342 and a Flash controller die 324 ontop of the substrate 322. FIG. 11 shows a side view of the layout ofFIG. 10.

The height of the spacer 345 and 445 is less than that of conventionalstacking Flash memory card design. The reason is that spacer height is afunction of the wire bonding loop height. The lower the loop height, thelower the spacer height is required. The loop height is also a functionof the lateral distance between the two bonding pads, as shown in FIG.12.

As shown in FIG. 12, the distance between pad A and pad B is DI 154. Thedistance between pad A and pad C is 02 153. The wires 151 and wire 152are for these two pairs of pads respectively. Their corresponding loopheights are HI 156 and H2 155 respectively. The shorter the lateraldistance DI 154, the lower the loop height HI 156 is necessary. Due tothe use of the interposer 342, the corresponding pads 327 and 326between interposer 342 and Flash memory dies 523, 423 and 323 can beright next to each other physically, as shown in FIG. 11. Thecorresponding pads 319 and 318 between interposer 342 and Flashcontroller die 324 can be right next to each other physically, as shownin FIG. 10. It therefore has the shortest wires possible between anycorresponding pads and thus creates the lowest deterministic loop heightpossible. The net effect of lower spacer 345 and 445 results in morestacking height possible for Flash memory dies 323, 423 and 523 andachieves more density on Flash memory card 321 as a consequence.

Alternate Exemplary Embodiment

One alternative embodiment is to place the controller unit to the middleof the Flash memory die and use direct die-to-die wire bonding evenwithout the need for an on-die interposer.

Yet another alternate embodiment is to form an on-die redistributionlayer on the Flash memory in lieu of the on-die interposer. The onlydifference is that a redistribution layer can be fabricated on the Flashmemory wafer, while the interposer is normally applied to the individualFlash memory die during substrate subassembly.

Another alternate embodiment is to use flexible substrate instead offlexible on-die interposer.

Advantages Over Prior Art

Unlike the conventional approach that brings all bonding wires from padson Flash controller and Flash memory dies to the substrate, a Flashmemory card in accordance with the present invention utilizes an on-dieinterposer, as shown in FIG. 6, to reduce the number of bonding wires.The interposer sits on top of the Flash memory die with bonding pads andtraces to connect among Flash controller die, Flash memory die and Flashcard interface, as shown in FIG. 7 and FIG. 8. Since the Flash cardinterface signals are limited in number (less than 10) and are usuallycontrolled by the Flash controller, they are the only signals that needto be wire-bonded to the substrate. This will dramatically reducewire-bonding pads on the substrate from about 50 to less than 10, areduction by 80%.

The bonding wire length in this invention is more uniformly distributedwith the on-die interposer than that of the conventional approach. Nobonding wires have to cross over other wires as with prior art in Flashmemory die stacking situation, as shown in FIG. 4.

Use of on-die interposer for wire-bond interconnect between the Flashmemory die and Flash controller effectively reduces wire-bond space onthe substrate and allows largest possible Flash memory die to be used onthe Flash memory card, as illustrated in the die size shown in FIG. 4(prior art) and FIG. 6 (present invention).

Use of an on-die imposer for direct wire-bond to save perimeterwire-bond space on the substrate.

Use of center-cutout on-die interposer to accommodate Flash controllerdie. It reduces overall height and allows more density as shown in FIG.9.

Use of flexible circuit on-die interposer to allow expandable Flashmemory die stacking.

The present invention also reduces bonding wire length throughconvenient interposer pads nearby. It further reduces the loop height ofbonding wire, allowing the use of spacers having less thickness. As aconsequence, more stacking of Flash memory dies can be achieved in thesame Flash memory card.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

1. A Flash memory card comprising: at least two wires; a substrate,wherein the substrate includes a first plurality of bonding pads; aFlash memory die on top of the substrate; a controller die on top of theFlash memory die; and a interposer coupled to the controller die and ontop of the Flash memory die, wherein the interposer includes a secondplurality of bonding pads, and wherein the second plurality of bondingpads of the interposer shifts wire bonding of the at least two wires tothe interposer and minimizes wire bonding of the at least two wires tothe substrate.
 2. The Flash memory card of claim 1 wherein theinterposer surrounds the controller die.
 3. The Flash memory card ofclaim 1 wherein the interposer is placed side by side with thecontroller die.
 4. The Flash memory card of claim 1 wherein theinterposer is on top of the controller.
 5. The Flash memory card ofclaim 2 which includes a second Flash memory die coupled to theinterposer and a spacer for separating the Flash memory die from thesecond Flash memory die.
 6. The Flash memory card of claim 1 wherein theinterposer includes at least one connecting trace.
 7. The Flash memorycard of claim 2 wherein the interposer includes a cut out in a middlearea large enough to accommodate the Flash controller die.
 8. The Flashmemory card of claim 1 wherein the interposer comprises a serpentineflexible memory on die member.
 9. The Flash memory card of claim 1wherein the interposer comprises an extended tab and a supporting standoff underneath the extended tab, wherein the extended tab hangs over theedge of the dies, and the wire bonding is used to connect from extendedtab portion of the interposer to a second interposer on an upper level.10. The Flash memory card of claim 2 wherein a height of the Flashcontroller die is minimized based upon the interposer surrounding theFlash controller die.
 11. The Flash memory card of claim 5 wherein aheight of the spacer is a function of a wire distance between bond padof the interposer and bond pads of the Flash memory die.
 12. A Flashmemory card comprising: at least two wires; a substrate, wherein thesubstrate includes a first plurality of bonding pads; a first Flashmemory die on top of the substrate; a Flash controller die on top of thefirst Flash memory die; a serpentine interposer coupled on top of thefirst Flash memory die, wherein the serpentine interposer includes asecond plurality of bonding pads, and wherein the second plurality ofbonding pads of the serpentine interposer shifts wire bonding of the atleast two wires to the interposer and minimizes wire bonding of the atleast two wires to the substrate; at least one other Flash memory die;wherein the Flash memory die is coupled to the serpentine interposer;and a spacer for separating the first Flash memory die from the secondFlash memory die.
 13. The Flash memory card of claim 11 wherein theserpentine interposer includes at least one connecting trace.
 14. TheFlash memory card of claim 11 wherein the serpentine interposer includesa cut out in a middle area large enough to accommodate the Flashcontroller die.
 15. A Flash memory card comprising: at least two wires;a substrate, wherein the substrate includes a first plurality of bondingpads; a first Flash memory die on top of the substrate; a Flashcontroller die on top of the first Flash memory die; an extended tabinterposer coupled on top of the first Flash memory die, wherein theextended tab interposer includes a second plurality of bonding pads, andwherein the second plurality of bonding pads of the extended tabinterposer shifts wire bonding of the at least two wires to theinterposer on an upper level and minimizes wire bonding of the at leasttwo wires to the substrate; a second Flash memory die; wherein thesecond Flash memory die is coupled to the extended tab interposer; and aspacer for separating the first Flash memory die from the second Flashmemory die.
 16. The Flash memory card of claim 15 wherein the extendedtab interposer includes at least one connecting trace.
 17. The Flashmemory card of claim 15 wherein the extended tab interposer includes acut out in a middle area large enough to accommodate the first andsecond Flash controller dies.